Formwork for Concrete Structures by R.L.Peurifoy and G.D- By EasyEngineering.net

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Forms for Thin-Shell Roof Slabs 387
FIGURE 13-3 Formwork for a circular shell roof using lumber.
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After the concrete has gained the desired strength, the decking
can be lowered several inches below the roof slab. If the entire structure
is to be lowered and moved longitudinally to a new location for
reuse, the 2 × 6 sills should be installed longitudinally instead of in
the position shown in order that the structure may slide on them.
Also, it may be desirable to use larger sills, such as 2 × 12. If the structure
is to be moved and reused, all braces and scabs should be left
intact.
Design of Forms and Centering for a Circular Shell Roof
Use the information shown in Figure 13-3, together with that given in
this section, to design the forms and centering for a circular shell roof.
The span is 30 ft and the rise is 5 ft. The thickness of the concrete slab
is 4 in. The live load will be 50 lb per sq ft. Use ¾-in. Class I Plyform
decking and No. 2 grade Southern Pine lumber.
Space the Joists
The spacing of the joists will be governed by the allowable span
length of the Plyform decking. The Plyform will be laid with the face
grain across the joists. The dead load of 4-in.-thick concrete having a
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